Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs

From: Joe Perches <joe@perches.com>
To: Kees Cook <keescook@chromium.org>
Cc: Denis Efremov <efremov@linux.com>,
	Julia Lawall <julia.lawall@inria.fr>,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	linux-kernel@vger.kernel.org, cocci <cocci@systeme.lip6.fr>,
	Alex Dewar <alex.dewar90@gmail.com>
Subject: Re: [Cocci] [PATCH] usb: atm: don't use snprintf() for sysfs attrs
Date: Fri, 28 Aug 2020 01:10:06 -0700	[thread overview]
Message-ID: <526af204ddf95f94012c6132d12693852bfe7442.camel@perches.com> (raw)
In-Reply-To: <202008280056.6442BCC@keescook>

On Fri, 2020-08-28 at 00:58 -0700, Kees Cook wrote:
> On Thu, Aug 27, 2020 at 09:12:06PM -0700, Joe Perches wrote:
> > Perhaps something like the below with a sample conversion
> > that uses single and multiple sysfs_emit uses.
> 
> On quick review, I like it. :)
> 
> > [...]
> > +int sysfs_emit(char *buf, char *pos, const char *fmt, ...)
> > +{
> > +	int len;
> > +	va_list args;
> > +
> > +	WARN(pos < buf, "pos < buf\n");
> > +	WARN(pos - buf >= PAGE_SIZE, "pos >= PAGE_SIZE (%tu > %lu)\n",
> > +	     pos - buf, PAGE_SIZE);
> > +	if (pos < buf || pos - buf >= PAGE_SIZE)
> > +		return 0;
> 
> This can be:
> 
> 	if (WARN(pos < buf, "pos < buf\n") ||
> 	    WARN(pos - buf >= PAGE_SIZE, "pos >= PAGE_SIZE (%tu > %lu)\n",
> 		 pos - buf, PAGE_SIZE))
> 		return 0;

I had some vague recollection that WARN could be compiled
away to nothing somehow.  True or false?

If false, sure, of course, it'd be faster too.